1. Field of the Invention
The present invention relates to a method of and an apparatus for developing an electrostatic latent image with a dry-type two-component developer while stabilizing the density of the developed image at all times.
2. Description of the Prior Art
FIG. 27 of the accompanying drawings illustrates an image developing apparatus which is generally employed for carrying out a method of developing an electrostatic latent image using a dry-type two-component developer. The image developing device includes a large toner tank 1 housing various agitating mechanisms such as an agitating roller 2, a feed screw 3, and an agitating separator 4. Toner which has been supplied from a toner hopper 5 is mixed with a carrier and agitated by these agitating mechanisms, and then delivered onto a developing roller 6 serving as a developer carrier, on which the toner is deposited as a magnetic brush layer. The thickness of the deposited developer or magnetic brush layer is limited by a doctor blade 7.
The developing roller 6 includes a sleeve 8 with a pluraltity of magnets 9 disposed therein. At least one of the sleeve 8 and the magnet assembly is rotated in one direction to move the magnetic brush on the circumferential surface of the sleeve 8 in a certain direction. The magnetic brush is brought into contact with a photosensitive body 10 to develop an electrostatic latent image thereon into a visible toner image. After the image has been developed, the magnetic brush is scraped off the developing roller 6 into the toner tank 1. The toner that has fallen into the toner tank 1 is agitated and mixed again by the agitating mechanisms.
The two-component developer or toner is required to be well agitated and mixed for uniform toner density or good toner charging. The conventional method and apparatus for developing electrostatic latent images using the two component developer are advantageous in that developed images are of good quality. However, the various agitating mechanisms are necessary for sufficiently agitating the developer, and a large space is required for defining an agitating passage in which the developer is agitated by those agitating mechanisms. Another problem is that the carrier of the developer is fatigued by the agitation of the developer, resulting in a reduction of carrier durability.
In order to eliminate the drawbacks of the image developing apparatus using the two-component developer, there have been proposed various image developing apparatus in which the developer is not mixed and agitated. One such image developing apparatus is of the self-balanced type as disclosed in U.S. Pat. No. 4,615,606 and includes a charging roller for depositing toner thereon, the charging roller contacting a magnetic brush to supply toner. In another image developing apparatus, a magnetic brush is employed to supply toner to a developing roller for forming a thin toner layer on the developing roller. The former image developing apparatus, however, presents problems in that the toner on the developing roller has irregular densities because uniform balancing forces cannot be obtained due to irregular charged amounts among toner particles and irregular toner particle diameters. With the latter apparatus, the toner or developer is still required to be well mixed and agitated.